Generally, electrostatic discharge (ESD) protection elements are installed at any input/output (I/O) and supply pad of an integrated circuit (IC) to protect against damage due to electrostatic discharge. These protection elements have to turn on immediately when a discharge occurs and have to limit the voltage overshoot efficiently. At the same time, these protection elements should not be damaged by the discharge itself, which forces several amps through the I/O and protection devices.
A well-known protection element is the (semiconductor) silicon controlled rectifier (SCR). The SCR consists of n+ and p+ contact areas and two attached lightly doped p and n areas between. While SCRs are very robust concerning the discharge current and allow a low voltage clamping at high current levels, there is typically a challenge to achieve a trigger voltage sufficiently low to protect the associated circuit.